The subject invention concerns a method of manufacturing reinforced as well as non-reinforced thermosetting resin products, preferably products of glass-fibre-reinforced polyester, by building up a laminate of layers of synthetic resin and reinforcement fibres, if such fibres are used, with the aid of spraying equipment, by spraying the synthetic resin and the reinforcement fibres, if any, onto the wall of a mould.
Laminates comprising polyester and glass-fibre are to-day produced by means of spray-application at atmospheric pressure. The method in accordance with the subject invention is based on controlled spraying or application at a partial vacuum, preferably with the aid of industrial robots.
One problem inherent in spray application processes carried out in environmental atmosphere is that considerable amounts of air are mixed into the laminate. As a result, lengthy and manual working operations are required to make the laminate more homogenous. Despite such working, large amounts of air still remain in laminates produced in accordance with the methods hitherto used, which is the immediate cause of penetration of moisture into the laminate and weakening of the chemical and mechanical strength thereof.
This is also to a great extent true in spray-application of so-called gel coat, in which case it is likewise of importance that this external coating is free of air and pores to prevent the above-mentioned moisture penetration and degradation.
The method hitherto used which includes rolling to achieve the homogenous character, i.e. to squeeze the air out of the laminate, is very time-consuming and inefficient. The resulting products are uneven and therefore often have poor competitive ability in comparison with products of wood and metal.
In the present method of treating laminates with the aid of a metal roller for homogenization purposes, the fibreglass is exposed to mechanical stress which bends or breaks the fibres. As a result, the mechanical strength of the finished laminate is reduced. In addition, there is a marked tendency that the fibre, when exposed to hard and intensive rolling, will migrate to the lower portion of the laminate while the upper portion thereof, including approximately 20 to 25% of the thickness of the laminate, will be very rich in polyester, i.e. will have lower fibreglass contents. This is not desirable, as the mechanical qualities of the surface layer thus are reduced.
In order to reduce these time-consuming rolling operations, there is a great deal of negligence in industry. For instance, in many cases layers of a thickness of between 3 and 4 millimeters are applied between each rolling (1 to 2 millimeters is actually recommended).
On account of air resistance and re-circulation of air from the mould, the glassfibres easily rise when the prior-art method is used. The result is an increase of the partial lamination effect, giving less tensile and bending strength, a problem which most manufacturers have difficulties in solving when using to-day's operational methods.
Because of the phenomenon outlined above concerning re-circulation of air, it is impossible to spray complex-shaped objects, such as narrow areas and keel structures, with the aid of hitherto conventional methods, both in the case of gel coat and fibreglass/polyester. In such cases, the gel coat must be applied manually and the laminates be laminated by hand. This means prolonged working times and increased costs.